Object information acquiring apparatus

ABSTRACT

An object information acquiring apparatus is used. This apparatus comprises: a light source configured to emit pulsed light of a plurality of wavelengths; a wavelength controller configured to switch the wavelength; a probe configured to receive an acoustic wave generated and propagated in an object subjected to the pulsed light emitted onto the object; a scan controller configured to move the probe within a predetermined scanning range; and an information processor configured to acquire information about the object by using a plurality of electric signals corresponding to the wavelengths of the pulsed light output from the probe at each reception position in the scanning area. The wavelength controller switches the wavelength of the pulsed light before the probe scans the entire scanning area while receiving at each reception position an acoustic wave corresponding to at least one of the wavelengths of the pulsed light.

TECHNICAL FIELD

The present invention relates to an object information acquiringapparatus.

BACKGROUND ART

Conventionally, an X-ray mammography apparatus has been known as animage diagnostic apparatus effective in discovering or diagnosing breastcancer. Also, in recent years, the method in which light energy istransmitted through an object, a photoacoustic signal generated as aresult of thermal expansion caused by the absorption of the light energyis received, and the inside of the object is imaged based on thephotoacoustic signal, has received attention. A photoacoustic signal isan acoustic wave such as an ultrasonic wave. In particular, this signalis also called a photoacoustic wave.

For the reception and processing of a photoacoustic signal, it ispreferable to receive the photoacoustic signal and convert it into anelectric signal. A photoacoustic signal is generally converted into anelectric signal by using a conversion element such as a CMUT (CapacitiveMicromachined Ultrasonic Transducer) produced using a piezoelectricelement or semiconductor technology. Actually, a probe in which morethan one such conversion element is arranged is usually used.

However, it is difficult in terms of cost and yield to manufacture aprobe of a size sufficient to simultaneously acquire photoacousticsignals from the entire breast. In order to overcome this problem, PTL1, for example, describes an ultrasonic diagnostic apparatus thatautomatically carries out mechanical scanning using an ultrasonic probeto receive photoacoustic signals, and reconstruct a three-dimensionalimage over a wide examination area.

Meanwhile, the technology for calculating the ratio of presentsubstances of different optical absorption spectra by usingphotoacoustic signals obtained by the emission of light of a pluralityof wavelengths has been studied.

For example, NPL 1 describes a method for calculating oxygen saturationor the like in blood by using a plurality of wavelengths, throughfocusing on the difference in optical absorption spectra betweenoxidized hemoglobin and reduced hemoglobin present in blood.

If absorption coefficients (μ_(a) ^(λ1), and μ_(a) ^(λ2)) correspondingto wavelengths λ1 and λ2 are used in a certain position, oxygensaturation (SO₂) is calculated from the expression (1) given below.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack & \; \\{\mspace{79mu} {{SO}_{2} = {\frac{\left\lbrack {HbO}_{2} \right\rbrack}{\left\lbrack {HbO}_{2} \right\rbrack + \lbrack{Hb}\rbrack} = \frac{{\mu_{a}^{\lambda \; 2}ɛ_{Hb}^{\lambda \; 1}} - {\mu_{a}^{\lambda \; 1}ɛ_{Hb}^{\lambda \; 2}}}{{\mu_{a}^{\lambda \; 1}\Delta \; ɛ_{Hb}^{\lambda \; 2}} - {\mu_{a}^{\lambda \; 2}\Delta \; ɛ_{Hb}^{\lambda \; 1}}}}}} & (1)\end{matrix}$

Here, [HbO₂] is the concentration of oxidized hemoglobin and [Hb] is theconcentration of reduced hemoglobin. Symbols ε_(Hb) ^(λ1) and ε_(Hb)^(λ2) are molar absorption coefficients of reduced hemoglobin atwavelengths λ1 and λ2 respectively. Symbols Δε_(Hb) ^(λ1) and Δε_(Hb)^(λ1) are values found by subtracting the molar absorption coefficientsof reduced hemoglobin from the molar absorption coefficients of oxidizedhemoglobin at wavelengths λ1 and λ2 respectively.

Also, PTL 2 describes an apparatus for measuring glucose concentrationby emitting two wavelengths.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent No. 4448189-   PTL 2: Japanese Patent Application Laid-Open No. 2010-139510

Non Patent Literature

-   NPL 1: Journal of Biomedical Optics 14(5), 054007

SUMMARY OF INVENTION Technical Problem

However, where mechanical scanning is carried out with a probe such thata plurality of wavelengths are emitted onto an observation area of acertain object and photoacoustic signals corresponding to thewavelengths are acquired, the problem may occur that the object movesduring scanning.

Imaging time (photoacoustic wave reception time) required to acquirephotoacoustic signals from an area (240 mm×180 mm) equal to a panel usedin general mammography is calculated in the manner described below. Asan example, it is assumed that the element size is 2 square mms, thenumber of reception CHs is 500 CHs, the repetition frequency of lightemission is 10 Hz, and the average is calculated from 256 measurementsin order to improve the reception signal SN ratio. In this case, bysimple arithmetic, (240×180×256) (2×2×500×10)=552.96 (secs), that is, animaging time of about 9 min is required in order to acquirephotoacoustic signals corresponding to one wavelength.

As described above, to calculate, for example, oxygen saturation,absorption coefficients corresponding to a plurality of wavelengths atfocused points are used. However, if there is a time difference of about9 mins between the point in time that a photoacoustic signal at afocused point is acquired using wavelength λ1 and the point in time thata photoacoustic signal at the focused point is acquired using wavelengthλ2, there is a high possibility of displacement of an object,especially, of a living biological object.

In order to calculate oxygen saturation or the like at a certain focusedpoint, absorption coefficients corresponding to wavelengths λ1 and λ2 atthe focused point have to be used. If there is displacement due to thetime difference between the points in time that data corresponding towavelength 71 is acquired (the point in time that a photoacoustic waveis received) and data corresponding to wavelength λ2 is acquired (thepoint in time that a photoacoustic wave is received), it means thatoxygen saturation is consequently calculated using absorptioncoefficients corresponding to different positions. This leads to errorin the calculation result, and degradation in reliability and accuracy.

The present invention has been proposed in view of the foregoingproblems. It is accordingly the object of the present invention toprovide a technology to prevent an object information acquiringapparatus, which acquires photoacoustic signals by using light of aplurality of wavelengths, from being affected by error due to objectmovement.

Solution to Problem

The present invention provides an object information acquiringapparatus, comprising:

a light source configured to emit pulsed light of a plurality ofwavelengths;

a wavelength controller configured to switch the wavelength of thepulsed light;

a probe configured to receive an acoustic wave generated and propagatedin an object subjected to the pulsed light emitted onto the object;

a scan controller configured to move the probe within a predeterminedscanning range; and

an information processor configured to acquire information about theobject by using a plurality of electric signals corresponding to thewavelengths of the pulsed light output from the probe at each receptionposition in the scanning area;

wherein the wavelength controller switches the wavelength of the pulsedlight before the probe scans the entire scanning area while receiving ateach reception position an acoustic wave corresponding to at least oneof the wavelengths of the pulsed light.

Advantageous Effects of Invention

The present invention is able to provide a technology to prevent anobject information acquiring apparatus, which acquires photoacousticsignals by using light of a plurality of wavelengths, from beingaffected by error due to object movement.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing the concept of dataacquisition using a plurality of wavelengths.

FIG. 2 is a diagram schematically showing probe movement that does notuse the present invention.

FIG. 3 is a time chart showing data acquisition that does not use thepresent invention.

FIG. 4 is a diagram schematically showing probe movement according tothe present invention.

FIG. 5 is a time chart showing data acquisition according to the presentinvention.

FIGS. 6A to 6C are diagrams showing the configuration of an ultrasonicdiagnostic apparatus according to the first embodiment.

FIG. 7 is a schematic view of a system according to the presentinvention.

FIGS. 8A and 8B are diagrams showing the configuration of an ultrasonicdiagnostic apparatus according to the second embodiment.

FIG. 9 is a diagram schematically showing probe movement according tothe second embodiment.

FIG. 10 is a time chart showing data acquisition according to the secondembodiment.

FIGS. 11A and 11B are diagrams showing the configuration of anultrasonic diagnostic apparatus according to the third embodiment.

FIG. 12 is a diagram schematically showing probe movement according tothe third embodiment.

FIG. 13 is a time chart showing data acquisition according to the thirdembodiment.

FIG. 14 is a diagram schematically showing a data acquisition rangeaccording to the present invention.

FIGS. 15A to 15C are time charts of data acquisition according to theexisting or present invention.

DESCRIPTION OF EMBODIMENTS

Referring to the accompanying drawings, preferred embodiments of thepresent invention will be described below.

An object information acquiring apparatus is an apparatus that uses aphotoacoustic effect in which an acoustic wave (typically ultrasonicwave) generated in an object by emitting light (electromagnetic wave)onto the object and propagated in this object is received andinformation about the object is acquired as image data. The acousticwave generated by photoacoustic effect is also called a photoacousticwave. Examples of object information include the initial acousticpressure of the acoustic wave, the density of light energy absorbed,absorption coefficient, information reflecting the concentrations ofsubstances composing the tissues in the object, and other information,all of which may be derived from the reception signals of acousticwaves. The concentrations of substances may be, for example, oxygensaturation, oxyhemoglobin/deoxyhemoglobin concentration, or glucoseconcentration. Additionally, object information may be acquired asnumerical or image data indicating distribution information at eachplace (i.e., each target point) in an object. That is, objectinformation may be acquired as image data indicating distributioninformation reflecting, for example, oxygen saturation distribution inan object.

The outline of a photoacoustic signal acquiring operation will now beexplained with reference to FIGS. 14 and 15.

FIG. 14 is a diagram schematically showing a data acquisition rangeaccording to the present invention. In the present invention, “the dataacquisition range” refers to a predetermined scanning range thatincludes a plurality of reception positions at which a probe receivesacoustic waves, and that is scanned in order that the probe receive aplurality of acoustic waves. This predetermined data acquisition rangemay be a range determined in advance or may be a range specified by auser every time. While scanning within this data acquisition range, theprobe receives acoustic waves, thereby making it possible to acquire, asimage data, three-dimensional object information, such as oxygensaturation distribution in an object. The probe 101 moves within thedata acquisition range 105 and receives photoacoustic waves. In thedescription below, such photoacoustic waves detected by the probe arecalled photoacoustic signals.

Here, it is assumed that photoacoustic signals corresponding to pulsedlight of two different wavelengths, λ1 and λ2, is acquired over the dataacquisition range 105. Where the present invention is not used, it isassumed that the operation is performed such that a photoacoustic signalcorresponding to pulsed light of wavelength λ1 is captured over theentire area of the data acquisition range 105, then, wavelengthswitching is carried out, and a photoacoustic signal corresponding topulsed light of wavelength λ2 is acquired over the entire dataacquisition range 105. As shown in FIG. 15A, the operation is composedof time 501 taken to acquire a photoacoustic signal corresponding topulsed light of wavelength λ1 and time 502 taken to acquire aphotoacoustic signal corresponding to pulsed light of wavelength λ2. Ifthe time required for the probe 101 to scan over the entire dataacquisition range 105 is represented by T, a time of 2T is required intotal. Additionally, there is an average difference of T between thetimes required to acquire photoacoustic signals corresponding to thedifferent wavelengths.

Next will be described data acquisition where the present invention isused. The data acquisition range 105 is divided into a partial dataacquisition range 400A and a partial data acquisition range 400B, whichare partial areas. Order of data acquisition is shown in FIG. 15B. Thatis, the following procedure may be performed: a photoacoustic signalcorresponding to pulsed light of wavelength λ1 (a first wavelength) isfirst acquired (501A) in the partial data acquisition range 400A, thenwavelength switching is carried out, and a photoacoustic signalcorresponding to pulsed light of wavelength λ2 (a second wavelength) isacquired (502A) in the partial data acquisition range 400A; next,wavelength switching is again carried out, a photoacoustic signalcorresponding to pulsed light of wavelength λ1 is acquired (501B) in thepartial data acquisition range 400B, then, wavelength switching iscarried out, and a photoacoustic signal corresponding to pulsed light ofwavelength λ2 is acquired (502B) in the partial data acquisition range400B. If the time required for the probe 101 to scan over the entiredata acquisition range 105 is represented by T, the total time requiredis 2T, which is the same as the above. However, the average differencebetween the times required to acquire photoacoustic signalscorresponding to the different wavelengths decreases to T/2.

That is, before a photoacoustic signal generated by emission of pulsedlight of one of two wavelengths is acquired over the entire acquisitionrange 105, the wavelength is switched to the other, and a photoacousticsignal is acquired using this wavelength. This means that beforecompleting a scan of the entire data acquisition range (scanning range)while receiving a photoacoustic wave corresponding to pulsed light ofone wavelength at each reception position, switching between thewavelengths of the pulsed light is carried out. This makes it possibleto reduce the difference between the times required to acquirephotoacoustic signals corresponding to the different wavelengths. Inthis case, wavelength switching is carried out three times.

In addition, there may be a case as shown in FIG. 15C. That is, thefollowing procedure may be performed: a photoacoustic signalcorresponding to pulsed light of wavelength λ1 is first acquired (501A)in a partial data acquisition range 400A, then wavelength switching iscarried out, and a photoacoustic signal corresponding to pulsed light ofwavelength λ2 is acquired (502A) in the partial data acquisition range400A; subsequently, a photoacoustic signal corresponding to pulsed lightof wavelength λ2 is acquired (502B) in the partial data acquisitionrange 400B, then, wavelength switching is carried out, and aphotoacoustic signal corresponding to pulsed light of wavelength λ1 isacquired (501B) in the partial data acquisition range 400B. In this casealso, the difference between the times required to acquire photoacousticsignals corresponding to the different wavelengths can be reduced justas in the above. In this case, wavelength switching is carried out twotimes.

If the entire data acquisition area is divided into an M number ofpartial data acquisition ranges (partial areas) (M≧2) in a case wherephotoacoustic signals are acquired with different wavelengths of N typesby using the present invention, the minimum value for the number ofwavelength switching times is (N−1)×M. In the preceding example, sincetwo types of wavelength are used and the entire data acquisition area isdivided into two partial data acquisition ranges, the minimum number oftimes is (2−1)×2=2.

Incidentally, where the present invention is not used, in which theentire data acquisition range is scanned with one wavelength and thenthe wavelength is switched to the other, the number of wavelengthswitching times is (N−1).

That is, before all data (acoustic waves) are acquired at all receptionpositions within a data acquisition range by the emission of pulsedlight of different wavelengths of N types, the wavelength is switched(N−1)×M times, thereby reducing the difference between the timesrequired to acquire photoacoustic signals corresponding to the differentwavelengths. That is to say, error due to movement of an object, whichaccompanies the passage of time, can be prevented.

First Embodiment

An embodiment of a biological information processing apparatus accordingto the present invention will be described in detail below withreference to the drawings.

First, the outline and operation of a system according to the presentembodiment will be explained and then a data acquiring operation will bedescribed.

FIG. 6 is a diagram of an ultrasonic diagnostic apparatus according tothe first embodiment of the present invention, and shows theconfiguration of parts around objects. Each of FIGS. 6A and 6B is across-sectional view of the apparatus as viewed from a directionperpendicular to the direction in which the object is compressed. FIG.6C is a plan view of a holding plate as viewed from a direction in whichthe object is compressed.

Each object (a breast in this embodiment) 104 is sandwiched and heldbetween two holding plates 103 (103 a and 103 b). A probe 101 isinstalled on the opposite side of the holding plate 103 a to the breast104. A light emission unit 102 is installed at the opposite side of theholding plate 103 b to the breast 104. The probe 101 and light emissionunit 102 move in a data acquisition range 105, as shown by a change fromFIG. 6A to FIG. 6B.

The object is not a component of any part of the object informationacquiring apparatus of the present invention. However, its explanationis as follows: if an object information acquiring apparatus is used fordiagnosis of malignant tumor, blood vessel disease, blood sugar level,or the like in a human being or animal or for follow-up to chemicaltreatment, a site other than a breast, such as a finger, hand or foot ofa human being or animal may be assumed to be an object.

FIG. 7 is a diagram showing the outline of a system of the presentembodiment. A laser light source 204 generates pulsed light (typically,100 nsec or shorter) of wavelength (typically 700 nm to approximately1100 nm) close to near-infrared, according to a timing control signalfrom a system controller 201 and a wavelength control signal from alaser wavelength controller 210. After transmission along an opticaltransmission path, these pulsed light are transmitted through theholding plate 103 (not shown) from the light emission unit 102 andemitted onto an object (not shown). Consequently, a light absorber inthe object absorbs the pulsed light and generates acoustic waves. In thepresent invention, light refers to electromagnetic waves includingvisible and infrared rays. According to the constituent to be measured,a specific wavelength may be selected. The laser wavelength controllerserves as a wavelength controller according to the present invention,and the laser light source serves as a light source according to thepresent invention.

The probe 101 has a plurality of conversion elements. Using theseconversion elements, the probe receives photoacoustic waves passedthrough the holding plate 103 and converts them into electric signals(reception signals). A reception circuit system 205 subjects receptionsignals output from the probe 101 to sampling and amplifying processesand converts these signals into digital signals (digitized receptionsignals).

Using data acquisition range information specified by the systemcontroller 201, a scan controller 211 controls the probe scanningmechanism 202 and the emission system scanning mechanism 203 and movesthe probe 101 and light emission unit 102. Then, light emission andphotoacoustic signal reception as described above are carried outrepeatedly.

A reconstruction block 206 performs an image reconstruction processusing information about probe position and so on input from the systemcontroller 201 and using digital signals input from the receptioncircuit system 205. This image reconstruction is a process forcalculating initial acoustic pressure distribution p (r) ofphotoacoustic waves in an object by using FBP (Filtered Back Projection)or the like, expressed by, for example, the formula (2) given below.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack & \; \\{\mspace{79mu} {{p(r)} = {{- \frac{1}{2\pi}}{\int_{S_{0}}^{\;}{\int{\frac{S_{0}}{r_{0}^{2}}\left\lbrack {{t\frac{\partial{p_{d}\left( {r_{0},t} \right)}}{\partial t}} + {2{p_{d}\left( {r_{0},t} \right)}}} \right\rbrack}_{t = {{{r - r_{0}}}/c}}}}}}} & (2)\end{matrix}$

wherein, dS₀ is the size of a detector, S₀ is the size of an apertureused for reconstruction, each P_(d) (r₀, t) is a signal received by thecorresponding conversion element, r₀ is the position of thecorresponding conversion element, and t is a reception time.

For each wavelength, a reconstruction data storing unit 207 holds theinitial acoustic pressure distributions reconstructed from differentwavelengths.

From this reconstruction data storing unit 207, a multi-wavelengthcomposing unit 208 receives initial acoustic pressure distribution datareconstructed from the different wavelengths, and performs computation,thereby calculating object information such as oxygen saturation.Glucose concentration can also be calculated by appropriatelycontrolling a plurality of different wavelengths. An image display unit209 displays an image by its being controlled by the system controller201. Examples of an image displayed may include, for example: an imageshowing the initial acoustic distribution or absorption coefficientdistribution calculated from photoacoustic signals acquired using onewavelength; and oxygen saturation calculated by the multi-wavelengthcomposing unit 208.

The process performed from the reconstruction block to themulti-wavelength composing unit corresponds to the process performed bythe information processor according to the present invention.

Next, the acquisition of photoacoustic signals by using a plurality ofwavelengths will be explained with reference to the drawings.

FIG. 1 schematically shows the outline of data acquisition. Withreference to this drawing, a description is given of the operation ofacquiring photoacoustic signals by using a plurality of wavelengths.

The probe 101 with the conversion elements moves, thereby acquiring data(acoustic waves) at respective positions within the data acquisitionrange 105. At this time, the probe moves in the data acquisition rangesuch that the probe 101 moves in main scan and sub-scan directions aplurality of times. If it is assumed that the probe moves in the mannerof a Raster scan, the main scan direction refers to the direction ofmovement along a scan line, that is, the direction in which the probemoves while receiving an acoustic signal at each reception position. Thesub-scan direction refers to the direction of movement between the scanlines, that is, the direction intersecting (typically, orthogonal to)the main scan direction. It is assumed that each partial dataacquisition range, which is acquired by one movement in the main scandirection, is assigned to 110A, 110B, 110C, and 110D. In the presentembodiment, the partial data acquisition ranges are areas into which thedata acquisition range, i.e., the scanning range, is divided in thesub-scanning direction. Additionally, each of the partial dataacquisition ranges 110A, 110B, 110C, and 110D is a range correspondingto a scanning orbit followed by the probe moving in the main scandirection within the data acquisition range while receiving an acousticwave at each reception position.

It is assumed that photoacoustic signals generated by the emissions ofpulsed light of two different wavelengths are acquired over the dataacquisition range 105. For example, where photoacoustic signals areacquired by the emissions of two wavelengths (λ1 and λ2), it isnecessary to acquire photoacoustic signals by emitting the wavelengthsof the two types to the four partial data acquisition ranges.

As a comparative example, an operation in which the present invention isnot used is explained with reference to FIG. 2.

First, a probe acquires data (acoustic waves) (indicated by thesolid-line arrow) by moving within the data acquisition range 105 whileemitting pulsed light of wavelength λ1. Then, the wavelength of thepulsed light is switched to λ2, and the probe is moved (indicated by thebroken-line arrow) within the data acquisition range 105.

FIG. 3 is a time chart showing the partial data acquisition ranges andemitted wavelengths in the cases where such movements are carried out.The symbols A, B, C, and D (301) on the axis represented by λ1 in thedrawing indicate timings of acquisition of the respective photoacousticsignals in the partial data acquisition ranges (110A, 110B, 110C, and110D) within which pulsed light of wavelength λ1 has been emitted.Additionally, A, B, C, and D (302) represent the timings of theacquisition of the respective photoacoustic signals in the partial dataacquisition ranges (110A, 110B, 110C, and 110D) within which pulsedlight of wavelength λ2 has been emitted.

In the moving method described above, by emitting one of the twodifferent wavelengths, all photoacoustic signals are acquired from thedata acquisition range 105.

Where such probe scanning is carried out, the acquisition intervalbetween the respective photoacoustic signals relating to wavelengths λ1and λ2 within the same partial data acquisition range (e.g., 110A) isindicated by t1.

FIG. 4 illustrates a data acquiring operation in which the presentinvention is used.

First, a wavelength control signal is transmitted to the laser lightsource 204 from the laser wavelength controller 210 and the wavelengthis set to λ1. A timing control signal for laser emission is transmittedfrom the system controller 201 and thereby the laser light source 204generates pulsed light of wavelength λ1. In response to a control signalfrom the scan controller 211, the probe 101 and light emission unit 102are moved in the main scan direction. In such a manner, photoacousticsignals corresponding to pulsed light of wavelength λ1 are acquired (thesolid-line arrow in 110A) within the partial data acquisition range110A. Subsequently, the probe 101 and light emission unit 102 areshifted to the sub-scan direction and moved within the partial dataacquisition range 101B. Then, while the probe 101 and light emissionunit 102 are moved in the main scan direction within the partial dataacquisition range 110B, light emission and data acquisition are carriedout (the solid-line arrow in 110B). Thus, data in the partial dataacquisition ranges 110A and 110B are acquired.

Next, a wavelength control signal is transmitted to the laser lightsource 204 from the laser wavelength controller 210 and the wavelengthis set to λ2. Thereafter, photoacoustic signals corresponding to pulsedlight of wavelength λ2 are acquired in the partial data acquisitionranges 110A, 110B, 110C, and 110D (broken-line arrows in 110A to 110D).

Subsequently, a wavelength control signal is again transmitted to thelaser light source 204 from the laser wavelength controller 210, and thewavelength is set to λ1. Then, photoacoustic signals corresponding topulsed light of wavelength λ1 are acquired within the data acquisitionranges 110C and 110D.

FIG. 5 is a time chart showing the partial data acquisition ranges andemitted wavelengths in a case where such movements have been performed.Each of the two dotted-lines between the axes λ1 and λ2 indicates thatwavelength switching has been carried out. That is, wavelength switchinghas been carried out two times. Specifically, electric signalscorresponding to the wavelengths of the pulsed light have been outputfrom the probe at their respective reception positions.

In probe scanning in the present embodiment, before all photoacousticsignals are acquired from within the data acquisition range 105 byemitting pulsed light of one of the two different wavelengths (forexample, λ1), the wavelength of pulsed light is switched. Also, at thepoints in time that the second and sixth movements in the main scandirection of the movements (eight times) in the main scan direction havebeen completed, the wavelength of pulsed light generated by the laserlight source 204 is switched.

In probe scanning in the present embodiment, the acquisition intervalbetween the respective photoacoustic signals relating to wavelengths λ1and λ2 within the same partial data acquisition range 110A is indicatedby t2. As described above, this acquisition interval is shorter than thecase where a photoacoustic signal corresponding to the emission ofpulsed light of wavelength λ1 and subsequently a photoacoustic signalcorresponding to the emission of pulsed light of wavelength λ2 areacquired within the entire data acquisition range 105. Accordingly, inthe present embodiment, interval t2 is half of t1.

Therefore, according to the present embodiment, error due to movement ofan object, which accompanies the passage of time, can be prevented.Accordingly, when oxygen saturation and so on are calculated usingreception signals corresponding to the two wavelengths (λ1 and λ2),error resulting from displacement is prevented, and a highly reliable,highly accurate image can be composed. In the present embodiment, twoinitial acoustic pressure distributions corresponding to the twowavelengths are obtained in advance, and then oxygen saturationdistribution is obtained. However, without obtaining these initialacoustic pressure distributions, oxygen saturation and so on can beobtained using electric signals (reception signals) output from theprobe when photoacoustic waves are received.

Also, in the present embodiment, the acquisition of data within eachpartial data acquisition range is completed by one movement in the mainscan direction. However, in order to obtain a required signal SN ratio,movement in the main scan direction may be carried out a plurality oftimes while pulsed light of the same wavelength is emitted. For example,even by exerting control such that movement in the sub-scan direction iscarried out after one forward and backward movement in the main scandirection, the same advantageous effect of the present invention can beobtained.

Second Embodiment

FIG. 8 shows diagrams of an ultrasonic diagnostic apparatus according tothe second embodiment of the present invention, and shows theconfiguration of parts around an object. FIG. 8B is a cross-sectionalview of the apparatus as viewed from a direction perpendicular to thedirection in which the object is compressed, and FIG. 8A is a plan viewof a holding plate as viewed from a direction in which the object iscompressed.

An object (a breast in the present embodiment) 104 is sandwiched andheld between two holding plates 103 (103 a and 103 b). A probe 101 isinstalled at the opposite side of the holding plate 103 a to the breast104. Alight emission unit 102 is installed at the opposite side of theholding plate 103 b to the breast 104. The probe 101 and light emissionunit 102 are moved so as to acquire data within a data acquisition range105.

The probe 101 moves in a circular direction 801, as a main scandirection, around an axis 803 in the object, and moves in a direction802, as a sub-scan direction, substantially perpendicular to the mainscan direction.

In order to receive acoustic waves transmitted through the holdingplates 103, a medium (e.g. water or caster oil) that transmitsultrasonic waves is injected between the probe 101 and holding plates103.

Since the outline of the system and the flow of data processing are thesame as those in the first embodiment, explanation thereof is omitted,and acquisition of photoacoustic signals by using a plurality ofwavelengths will be explained with reference to the drawings.

FIG. 9 illustrates a data acquiring operation that is performed in thepresent embodiment. The main scan direction is a circular directionaround the axis 803, as described above. However, here, atwo-dimensional drawing in which the circular directions are developedin plane is used for ease of explanation.

In the present embodiment, a description will be given of a case wherethree wavelengths are used.

First, a wavelength is set to λ1 and the probe 101 is moved in the mainscan direction, thereby acquiring a photoacoustic signal correspondingto pulsed light of wavelength λ1 (solid-line arrow) within a partialdata acquisition range 110A. Subsequently, the wavelength is switched toλ2, and a photoacoustic signal corresponding to pulsed light ofwavelength λ2 is acquired (broken-line arrow) in the partial dataacquisition range 110A. Further, the wavelength is switched to λ3 and,then, a photoacoustic signal corresponding to pulsed light of wavelengthλ3 is acquired (chain-line arrow) in the partial data acquisition range110A. Thereafter, the probe shifts to the sub-scan direction, andacquires data within the partial data acquisition range 110B. Byrepeating such an operation, data up to a partial data acquisition range110D may be acquired.

As described above, before shifting to the sub-scan direction, movementin the main scan direction is carried out (at least twice, specificallythree times in the present embodiment), and control for wavelengthchange is exerted at the time point in time that one of the movements inthe main scan direction has been completed.

FIG. 10 is a time chart showing the partial data acquisition ranges andemitted wavelengths, according to the present embodiment. In probescanning in the present embodiment, the acquisition interval between therespective photoacoustic signals relating to wavelengths λ1 and λ3within the same partial data acquisition range 110A, is indicated by t3.This acquisition interval is notably shorter than the case where, afterphotoacoustic signals corresponding to the emission of pulsed light ofwavelength λ1 are acquired in the entire data acquisition range 105,photoacoustic signals corresponding to emission of pulsed light of thewavelength λ2 and photoacoustic signals corresponding to emission ofpulsed light of the wavelength λ3 are acquired. In the presentembodiment, the time difference is reduced to ¼ of the case in which thepresent invention is not used.

According to the present embodiment, wavelength switching and movementin the main scan direction are carried a plurality of times beforeshifting to the sub-scan direction. Therefore, acquisition intervalsbetween the photoacoustic signals corresponding to different wavelengthswithin the same partial data acquisition range can be further shortened.That is, error due to movement of an object, which accompanies thepassage of time, can be further reduced.

Therefore, by use of data reconstructed from photoacoustic signalsobtained from the wavelengths (λ1, λ2, and λ3), error resulting fromdisplacement is further reduced when oxygen saturation and so on arecalculated in the multi-wavelength composing unit. Accordingly, a morereliable, highly accurate image can be composed.

In the present embodiment, the main scan direction is specified ascircular direction around the axis. However, even where the probe isused for two-dimensional scanning as in spatial arrangement of the firstembodiment, the advantageous effects of the present invention can beobtained.

Third Embodiment

FIG. 11 is a diagram of an ultrasonic diagnostic apparatus according tothe third embodiment of the present invention, and shows theconfiguration of parts around an object. FIGS. 11A and 11B are diagramsof the object sagging, as viewed from one side and from aboverespectively.

An object (a breast in the present invention) 104 is allowed to sag. Aprobe 101 and a light emission unit 102 are installed in oppositepositions with the object 104 between them. The probe 101 and lightemission unit 102 are moved so as to acquire data within a dataacquisition range.

The probe 101 moves in a circular direction 801, as a main scandirection, around an axis 803 through the object, and moves in adirection 802, as a sub-scan direction, substantially perpendicular tothe main scan direction. In the present embodiment, the data acquisitionrange is a range obtained by moving in a sub-scan direction a plane inwhich the probe 101 is rotated 360° around the axis 803.

In order to receive photoacoustic waves generated in the object 104, amedium (e.g. water or caster oil) that transmits ultrasonic waves isinjected between the probe 101 and subject 104.

Since the outline of the system and the flow of data processing are thesame as those in the first embodiment, explanation thereof is omitted,and acquisition of photoacoustic signals by using a plurality ofwavelengths will be explained with reference to the drawings.

FIG. 12 illustrates a data acquiring operation that is performed in thepresent embodiment. The main scan direction is a circular directionaround the axis 803, as described above. However, here, atwo-dimensional drawing in which circular direction are developed in aplane is used for ease of explanation. That is to say, the right andleft ends of the data acquisition range 105 in FIG. 12 are continuouswith each other.

First, the probe 101 is rotated 360° (indicated by the hollow-line arrowin 150A) around the axis 803. During movement in this main scandirection, wavelength switching is carried out. In the presentembodiment, wavelength is switched for each pulse. That is, switchingtakes place in the following order: λ1, λ2, λ1, λ2, and so on. In orderto speedily change the wavelength of pulsed light generated by laserlight source, two lasers may be used alternately.

Such an operation makes it possible to acquire photoacoustic signalscorresponding to pulsed light of wavelengths λ1 and λ2 within thepartial data acquisition range 110A. At the time that the probe 101 hasbeen rotated 360° around the axis 803, the probe 101 is shifted to thesub-scan direction, and the probe 101 is again rotated 360° (thehollow-line arrow in 150B) around the axis 803, thereby acquiring datawithin a partial data acquisition range 110B. Data are acquired forpartial data acquisition ranges 110C and 110D in a similar manner.

While movement in the main scan direction is carried out in such amanner, control is exerted to switch the wavelength of pulsed lightgenerated by laser light source, and the data is acquired from the dataacquisition range.

FIG. 13 is a time chart showing emitted wavelengths. The range of 160Aschematically shows the period for which wavelength switching is carriedout for each pulse and each photoacoustic signal corresponding to pulsedlight of wavelength λ1 and each photoacoustic signal corresponding topulsed light of wavelength λ2 are acquired within a partial dataacquisition range 110A. Similarly, the ranges 160B, 160C, and 160Dcorrespond to 110B, 110C, and 110D.

In probe scanning in the present embodiment, the acquisition intervalbetween photoacoustic signals corresponding to the wavelengths λ1 and λ2within the same partial data acquisition range is indicated by t4. Thisacquisition interval is notably shorter compared to that where, afterphotoacoustic signals corresponding to emissions of pulsed light ofwavelength λ1 are acquired within the entire data acquisition range,photoacoustic signals corresponding to emissions of pulsed light of thewavelength λ2 are acquired.

According to the present embodiment, since wavelength switching iscarried out during movement in the main scan direction, acquisitioninterval between photoacoustic signals corresponding to differentwavelengths can be further shortened within the same partial dataacquisition range. That is, error due to movement of an object, whichaccompanies the passage of time, can be further reduced.

Therefore, by use of data reconstructed from photoacoustic signalsobtained from the plurality of wavelengths (λ1 and λ2), error resultingfrom displacement is further reduced when oxygen saturation and so onare calculated in the multi-wavelength composing unit. Accordingly, amore reliable, highly accurate image can be composed.

In the present embodiment, while the probe is continuously moved in themain scan direction, wavelength switching and acquisition ofphotoacoustic signals are carried out. Specifically, in movement in themain scan direction, the probe is not stopped at each reception positionbut is moved at almost constant speed. Therefore, as shown in FIG. 13,the acquisition position (reception position) of a photoacoustic signalwhen light of wavelength λ1 is emitted and that when light of wavelengthλ2 is emitted do not coincide exactly. However, if the frequency ofpulsed light is sufficiently high, processing can substantially proceedwithout taking differences between acquisition positions intoconsideration. Additionally, even if the acquisition position of aphotoacoustic signal corresponding to each light pulse is displaced,image data in a fixed area within each partial data acquisition range iscalculated in the reconstruction block 206. Therefore, imagereconstruction corresponding to the same position can be achieved.

Alternatively, the probe may be stopped at one position on an object, inwhich case, photoacoustic signals are received by using light ofwavelengths λ1 and λ2, and then the probe may be moved in the nextposition. In this case, photoacoustic signals with almost no timedifference can be acquired at the same reception position with respectto the object.

In the present embodiment, the main scan direction is specified as acircular direction around the axis. However, even where the probe isused for two-dimensional scanning, as in spatial arrangement of thefirst embodiment, the advantageous effects of the present invention canbe obtained.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2011-183574, filed on Aug. 25, 2011, which is hereby incorporated byreference herein in its entirety.

1. An object information acquiring apparatus, comprising: a pulsed-lightsource, configured to emit pulsed light of a plurality of wavelengths; awavelength controller configured to switch the wavelength of the pulsedlight; a probe configured to receive an acoustic wave generated in anobject irradiated with the pulsed light from said pulsed-light source; ascan controller configured to move said probe within a predeterminedscanning range; and an information processor configured to acquireinformation about the object by using a plurality of electric signals,corresponding to the wavelengths of the pulsed light output from saidthe probe at each reception position in the scanning area, wherein saidwavelength controller switches the wavelength of the pulsed light beforesaid probe scans the entire scanning area while receiving at eachreception position an acoustic wave corresponding to at least one of thewavelengths of the pulsed light.
 2. The object information acquiringapparatus according to claim 1, wherein said scan controller enablessaid probe to receive an acoustic wave within the scanning range bymoving said probe in a main scan direction and a sub-scan directionintersecting the main scan direction, the main scan direction being adirection said which the probe is moved while receiving an acoustic waveat each reception position.
 3. The object information acquiringapparatus according to claim 2, wherein the scanning range is dividedinto a plurality of partial areas in the sub-scan direction, and whereinafter said probe receives an acoustic wave corresponding to pulsed lightof a first wavelength at each reception position in at least one partialarea but before said probe receives an acoustic wave in the otherpartial areas, said wavelength controller switches the wavelength of thepulsed light to a second wavelength different from the first wavelength.4. The object information acquiring apparatus according to claim 3,wherein the partial areas correspond to scanning orbits followed whensaid probe is moved while receiving an acoustic wave at each receptionposition in the main scan direction within the scanning range, whereinsaid scan controller moves said probe a plurality of times within thepartial area, and wherein said wavelength controller switches thewavelength of the pulsed light so that pulsed light of a differentwavelength is emitted each time said probe is so moved.
 5. The objectinformation acquiring apparatus according to claim 3, wherein thepartial areas correspond scanning orbits followed when said probe ismoved while receiving an acoustic wave at each reception position in themain scan direction within the scanning range, and wherein saidwavelength controller switches the wavelength of the pulsed light whilesaid probe moves in the main scan direction in the partial areas.
 6. Theobject information acquiring apparatus according to claim 5, whereinsaid wavelength controller switches the wavelength of the pulsed lighteach time the pulsed light is emitted.
 7. The object informationacquiring apparatus according to claim 1, wherein said wavelengthcontroller switches the wavelength of the pulsed light between twodifferent wavelengths.
 8. The object information acquiring apparatusaccording to claim 1, wherein said wavelength controller switches thewavelength of the pulsed light between three different wavelengths. 9.The object information acquiring apparatus according to claim 1, whereinsaid pulsed-light source emits the pulsed light having wavelengths inthe range of from 700 nm to 1100 nm.
 10. The object informationacquiring apparatus according to claim 1, wherein said informationprocessor acquires at least any one of initial acoustic pressure of theacoustic wave, density of light energy absorbed, absorption coefficient,and information reflecting the concentrations of substances.